The present invention relates to method and apparatus for forming a sheet of extruded deformable polymer, and relates, more particularly, to method and apparatus for so forming such a sheet with a plurality of longitudinally extending fracture lines along which the sheet may be split to thereby sub-divide the sheet into tapes, ribbons or filaments.
In commercial usage the term "sheet" is often employed to designate heavier gauge material, say 0.010 inches, and which may be provided in discrete lengths while the term "film" usually refers to lighter gauge materials of substantial length. Notwithstanding these distinctions which are found in commercial practice the term "sheet" as utilized herein is intended to mean both sheet and film material whatever the length and thickness thereof might be.
Synthetic textile strand material requires the production of high quantity, smooth, well-defined, fine denier filaments. The conventional way of insuring this is by extruding a group of monofilaments from a spinneret. This requires highly specialized and expensive equipment to get useful production of the fibers. A more recent approach has been to advance an extruded deformable polymer sheet from extrusion apparatus and as a continuous process emboss or profile the sheet in a predetermined pattern such that controlled splitting into smooth, uniform multi-filamentary yarn is achieved. A typical apparatus for achieving this result employs a positively driven roll embossed with a plurality of ridges and grooves extending at spaced apart intervals around the periphery of the roller. A backing roll cooperates with the embossing roll to form a pinch line or nip through which the extruded sheet is advanced so that the polymer sheet has the configuration of the embossing roll formed therein. After embossing the sheet is continuously advanced to further processing steps where it is fibrillated or split by suitable mechanical means along the embossed fracture lines to firstly provide a series of tapes with the tapes thereafter being further split to provide monofilaments which lend themselves to further processing into textile end products.
While the embossing technique as just related functions admirably to provide high speed production of monofilaments, it has been found that, due to the inherent memory in the polymer sheet, after it is embossed the fracture lines in the sheet tend to lose some of their definition. That is to say, the ribs which are formed in the sheet thicken so that the desired denier as defined by the embossments on the embossing roll is altered and, further, the webs lightly joining the ribs together thicken as the polymer sheet attempts to return to its original character. These conditions, of course, is undesirable in that the monofilamentary material ultimately produced by the embossing process is of somewhat unpredictable denier and, additionally, fracturing of the sheet into its constituent tapes and monofilaments is made more difficult by virtue of the alteration of the fracture lines.